To perform optimal control of the fuel supply amount and ignition timing of an internal combustion engine, or to estimate generated torque accurately, the temperature of gas in the cylinder at the point in time when an intake valve closes or when the compression stroke begins must be determined accurately.
As a technique of estimating the temperature of intake gas in the cylinder, Tokkai Hei 09-189256, published by the Japan Patent Office in 1998, teaches a method in which an amount of residual heat is calculated by subtracting the amount of heat discharged from the engine room from the amount of heat generated in the internal combustion engine per unit time, and an amount of heat transmitted to the intake air aspirated into the cylinder is estimated on the basis of the amount of residual heat. The prior art also teaches a method in which an amount of heat transmitted to the intake system is estimated from the amount of accumulated heat in the engine main body, represented by the coolant temperature, and the temperature of the intake gas in the cylinder is estimated by correcting the outside air temperature on the basis of the amount of heat transmitted to the intake system.
Tokkai Hei 05-180057, published by the Japan Patent Office in 1993, teaches a method of estimating the intake gas temperature in a cylinder from the pressure in an intake pipe of the internal combustion engine, the amount of air passing through a throttle, and the volume of the intake pipe from the throttle to the intake valve, using an equation of state.
Tokkai Hei 11-148419, published by the Japan Patent Office in 1999, teaches a method in which the gas inside the engine is considered as a mixture of intake gas and residual gas, and the temperature of the gas in the cylinder is calculated from the temperature and mass of the intake gas and the temperature and mass of the residual gas using a predetermined computing expression.